yade-dev team mailing list archive

[Chiara Modenese <c.modenese@xxxxxxxxx>]

On 7 July 2011 13:58, Christian Jakob <806944@xxxxxxxxxxxxxxxxxx> wrote:

> OK, for following results of further calculations the shear modulus is
> always 3e7 and poisson ratio is always 0.3.
> Note also, that viscous damping in shear direction doesnt influence the
> flyback_height.
>
Of course.

> initial height is always 0.133
>
>
> case 1: no local damping, viscous damping normal = 0.015
>
> YADE: flyback_height                       = 0.1198912649
> PFC (notension on): flyback_height = 0.12361
> PFC (notension off): flyback_height = 0.12354
>
So the problem is not the tension on or off. Can you check that the damping
coefficients are defined in the same way for both codes? That could be the
cause of the difference then.

>
>
> case2: local damping = 0.01, no viscous damping
>
> YADE: flyback_height                       = 0.127960977322
> PFC (notension on): flyback_height = 0.12769
> PFC (notension off): flyback_height = 0.12769
>

>
> case3: no damping at all
>
> YADE: flyback_height                       = 0.133156194762
> PFC (notension on): flyback_height = 0.1329
> PFC (notension off): flyback_height = 0.1329
>
In case 2 and 3 we should get the same result, I think. Am not sure what
could be the cause.
Hint 1) Can you try to compare the numbers step by step, having exactly the
same configuration and time step?
Hint 2) Can you try to do the same test but with the simple linear elastic
law and no damping at all?
Also I would just suggest to do a much simpler test where you just study the
contact between two balls and record velocities, positions etc in every time
step. Let me know.
Bruno, what do you think about the above numbers?

>
> ...hope it helps ...
>
> I do not understand where the attractive force (in PFC notension off) comes
> from, but the influence on the results is very low (see case1).
>
The attractive force comes from the damper.

> What is default in YADE, notension on or off?
>
In YADE, at least in the HertzMindlin contact law, the default and also only
option for the moment is notension off. Actually, I will add this option
because it is quite important.

Chiara

>
>
> Christian
>
> --
> You received this bug notification because you are a member of Yade
> developers, which is the registrant for Yade.
> https://bugs.launchpad.net/bugs/806944
>
> Title:
>  different behavoir of Hertz model while comparing PFC and YADE
>
> Status in Yet Another Dynamic Engine:
>  New
>
> Bug description:
>  Hello,
>
>  During verifiing my model I compared output from PFC 4.0 with the
>  output from YADE (bzr2877 on Debian Squeeze 64bit). There I found a
>  different behavior between these two programs. I dont know if this is
>  a bug or not, but I hope someone can explain the different behavior.
>
>  The model itself is very simple. There are two spheres, an upper one and a
> lower one. The lower one is fixed and the upper one is falling down to the
> lower one, collides and jumps back. The value of interest is the flyback
> height of the upper particle.
>  In PFC I measure higher values of flyback height, then in YADE (see
> log-files in the attachment).
>
>  Can someone tell me why there is a difference in the flyback height?
>  (input parameters are the same for both programs ... see
> caller_two-spheres-jumping.dat for PFC and two-spheres.py for YADE)
>
>  Regards,
>
>  Christian Jakob
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/yade/+bug/806944/+subscriptions
>
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-- 
You received this bug notification because you are a member of Yade
developers, which is the registrant for Yade.
https://bugs.launchpad.net/bugs/806944

Title:
  different behavoir of Hertz model while comparing PFC and YADE

Status in Yet Another Dynamic Engine:
  New

Bug description:
  Hello,

  During verifiing my model I compared output from PFC 4.0 with the
  output from YADE (bzr2877 on Debian Squeeze 64bit). There I found a
  different behavior between these two programs. I dont know if this is
  a bug or not, but I hope someone can explain the different behavior.

  The model itself is very simple. There are two spheres, an upper one and a lower one. The lower one is fixed and the upper one is falling down to the lower one, collides and jumps back. The value of interest is the flyback height of the upper particle.
  In PFC I measure higher values of flyback height, then in YADE (see log-files in the attachment).

  Can someone tell me why there is a difference in the flyback height?
  (input parameters are the same for both programs ... see caller_two-spheres-jumping.dat for PFC and two-spheres.py for YADE)

  Regards,

  Christian Jakob

To manage notifications about this bug go to:
https://bugs.launchpad.net/yade/+bug/806944/+subscriptions